The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
Whenever a tooth's enamel or cementum does not fully cover the dentin, hot or cold liquids and foods and even cold air can cause nerve irritation (dentin hypersensitivity) that causes a short, sharp pain. Causes of Sensitive Teeth. There are many reasons why your teeth may be sensitive.